forensic investigation

Forensic Science

Any science used for the purpose of the law. It applies scientific knowledge to legal investigations, civil disputes, criminal laws, government regulations, and public health.

Forensis

Latin term meaning public, to the forum, public discussion, argumentative, rhetorical, or belonging to debate or discussion.

Modern Meaning of Forensic

Used in or suitable to a court of law.

Why Forensic Science Is Not a Single Science

It contains many different branches of science that can be applied to legal investigations.

Forensic Biology

The application of biology to forensic investigations, including DNA typing, microbiology, biological evidence, and death investigations.

Forensic Chemistry

The application of chemistry to forensic investigations, including toxicology, drugs, alcohol, unknown substances, death investigations, and trace evidence.

Forensic Physics

The application of physics to forensic investigations, including measurements, bloodstain pattern analysis, trajectory analysis, and large

Forensic Anthropology

The application of anthropology to legal investigations, especially the examination and recovery of human bones and skeletal remains.

Forensic Entomology

is the study of insects in relation to forensic investigations.
Insects become associated with a body as decomposition occurs.
Different insects have different life cycles.
Scientists can use insect development to help estimate the time since death.

Applied Science

Science that uses knowledge from basic sciences to solve practical problems.

Basic Science

Science that develops general scientific knowledge, such as biology, chemistry, physics, and anthropology.

Generalist

A forensic professional with knowledge or responsibilities across multiple areas of forensic science.

Specialist

A forensic professional who focuses on a particular area of forensic science.

Forensic Anthropology and Human Remains

Forensic anthropologists examine bones and skeletal remains to estimate characteristics such as probable sex, approximate age, and other identifying information.

Forensic Entomology and Time Since Death

so their developmental stages can help estimate how long a body has been decomposing.

Forensic Physics Uses

Measurements, bloodstain pattern analysis, trajectory analysis, and crime scene reconstruction.

CSI Effect

The way forensic science portrayed on television and other media affects public perceptions and expectations of real forensic science.

Origin of the Term CSI Effect

The term was used in a 2004 USA Today article by R. Willing.

CSI Effect and Public Expectations

Television can create unrealistic expectations about scientific technology, accessibility, effectiveness, timing, the legal system, and forensic evidence.

CSI Effect Pros

Increased interest in forensic/STEM careers, more women entering the field, increased diversity, more interdisciplinary collaboration, and encouragement of lifelong learning.

TV Forensic Science

TV often shows experts quickly identifying evidence, receiving immediate DNA results, and reaching definite conclusions quickly.

Real Forensic Science

Evidence must be carefully collected, identified, tested, analyzed, and interpreted using multiple scientific procedures, which can take significant time.

Possible Forensic Results

Results may be inclusive, exclusive, or inconclusive/indeterminate rather than always providing a definite answer.

Blood Evidence

A red substance should not automatically be assumed to be blood; it must be scientifically tested.

Blood Evidence Testing Process

Test whether the substance is blood → determine whether it is human or non

Myth: Forensic Scientists Always Find Conclusive Evidence

Reality: forensic scientists objectively analyze and report their findings even when the results are inconclusive.

Myth: Forensic Science Is Infallible

Reality: forensic science depends on scientific principles such as reproducibility, falsifiability/testability, and peer review and can still have limitations or errors.

Myth: Forensic Scientists Work Only for Law Enforcement

Reality: forensic scientists may provide evidence or testimony for either the prosecution or defense.

Myth: Forensic Scientists Are Biased Toward the Prosecution

Reality: forensic scientists should objectively base conclusions on scientific methods and evidence rather than outside influence.

Forensic Science vs. Criminology vs. Criminal Justice

Forensic science analyzes scientific/physical evidence; criminology studies crime and criminal behavior; criminal justice deals with law enforcement, courts, corrections, and justice system processes.

Criminology

A social science that studies crime, criminal behavior, psychological tendencies, background factors, social factors, and why people may commit crimes.

Criminal Justice

The systems and processes used to respond to crime, including law enforcement, courts, prosecution, corrections, and other justice processes.

Scientific Process in Forensic Science

Forensic science relies on reproducibility, falsifiability/testability, and peer review.

Reproducibility

When an appropriate experiment or analysis is repeated, qualified scientists should obtain comparable results.

Falsifiability

A scientific claim must be testable in a way that could potentially demonstrate that it is wrong.

Peer Review

Evaluation of scientific methods, results, and conclusions by other qualified scientists to help ensure reliability.

Fingerprint Evidence Limitation

A person’s fingerprint at a crime scene establishes an association but does not automatically prove that the person committed the crime or establish when the fingerprint was left.

Bias

An inclination, conscious or unconscious, that favors one thing over another.

Bias in Forensic Science

Forensic scientists must remain objective and prevent outside information or influence from improperly affecting their scientific conclusions.

Blind Analysis

Providing samples to analysts as unknowns so they do not know unnecessary information about the people or case, helping reduce bias.

Sequential Unmasking

A method of controlling when contextual information is provided to an analyst to reduce potential bias.

Why Objectivity Matters in Forensic Science

Forensic conclusions can affect arrests, prosecution, convictions, people’s freedom, and public confidence in the justice system.

Accreditation

Evaluation of a laboratory or organization to determine whether it meets established standards for procedures, equipment, facilities, management, quality control, and quality assurance.

Accreditation Memory Trick

Accreditation = LAB.

Certification

A process showing that an individual has met professional requirements in a specific forensic specialty, which may include education, training, examinations, and recertification.

Certification Memory Trick

Certification = PERSON.

Accreditation vs. Certification

Accreditation applies to a laboratory or organization; certification applies to an individual.

ASCLD/LAB

American Society of Crime Laboratory Directors/Laboratory Accreditation Board; an example associated with crime laboratory accreditation.

Legal System vs. Scientific Method

The legal system is adversarial and relies on legal rules and precedent, while science is dynamic, iterative, evidence

Role of Forensic Scientist in Court

Forensic scientists analyze and explain scientific evidence but do not determine guilt or innocence.

Ethics in Forensic Science

Principles requiring forensic scientists to work accurately, objectively, honestly, and responsibly because their conclusions can significantly affect people’s lives.

Forensic Science Code of Ethics

There is no single universal code of ethics for all forensic science, and different interpretations do not automatically mean someone acted unethically.

Role of Accreditation and Certification in Ethics

Accreditation and certification organizations help uphold professional and ethical standards through standardized and validated practices.

Evidence

The “stuff” of forensic science; anything or any person that provides information about an event or crime scene.

How Evidence Is Generated

Evidence can be created during interactions among people, objects, and environments.

Role of Forensic Scientists With Evidence

Forensic scientists examine and interpret evidence using scientific methods.

Role of Legal System With Evidence

The legal system determines whether evidence can be admitted and used in court.

What Evidence Can Help Establish

Who was associated with a scene, what happened, how something happened, and the possible sequence of events.

Three Forms of Evidence

Physical evidence, testimonial evidence, and opinion evidence.

Examples of Evidence

Blood, fibers, fingerprints, firearms, glass, biological samples, footprints, shoe prints, tool marks, impressions, bullets, cartridge cases, hair, soil, grass, plant material, skin cells, and witness statements.

Physical Evidence

Nonliving material or objects associated with a crime, such as fingerprints, footprints, shoe impressions, tool marks, firearms, bullets, and cartridge cases.

Biological Evidence

Evidence originating from living organisms or biological material, such as blood, semen, saliva, hair, plant material, and other biological samples.

Testimonial Evidence

Information provided through statements or testimony from witnesses or other people.

Opinion Evidence

Evidence involving an opinion or interpretation, often provided by a qualified expert.

Locard’s Exchange Principle

“Every contact leaves a trace”; contact between people, objects, and scenes can result in the transfer of material.

Edmond Locard

Forensic scientist associated with Locard’s Exchange Principle; lived from 1877–1966.

Person to Scene Transfer

Examples include fingerprints, DNA, hair, fibers, and footwear impressions left by a person at a scene.

Scene to Person Transfer

Examples include soil, grass, glass, fibers, or biological material transferred from the scene onto a person.

Transfer Evidence

Material transferred when people, objects, or environments come into contact.

Transfer Evidence Limitation

Transfer can establish an association but does not automatically establish when, why, or how contact occurred or whether someone was present during the crime.

Inclusive Evidence

Supports including a person or object among the possible sources.

Exclusive Evidence

Supports excluding a person, object, or possibility as a source.

Indeterminate Evidence

Does not provide enough useful information to answer the question.

Context of Evidence

Evidence must be interpreted with other information from the case rather than in isolation.

One Event Can Produce Many Types of Evidence

A single event may generate gunshot residue, firearms, bullets, cartridge cases, blood, bloodstain patterns, fingerprints, bullet holes, glass fractures, and witness testimony.

Firearm Evidence

Bullets and cartridge cases can receive marks from a firearm that may provide information about the firearm involved.

Bloodstain Pattern Evidence

Blood patterns may provide information about movement, direction, locations, and possible sequence of events.

Glass Fracture Evidence

Fracture patterns may provide information about the direction or angle of impact and which side of the glass was struck.

Entry Wound

The location where a bullet enters the body.

Exit Wound

The location where a bullet leaves the body.

Why a Bullet May Not Produce an Exit Wound

A bullet can lose energy while traveling through the body and become lodged inside.

Evidence Links

Evidence can create associations between a person, object, and scene.

Inculpatory Evidence

Evidence that tends to include or incriminate a person.

Exculpatory Evidence

Evidence that tends to exclude or exonerate a person.

Direct Evidence

Evidence that addresses a fact without requiring additional inference.

Circumstantial Evidence

Evidence that requires inference to connect it to a conclusion.

Is Circumstantial Evidence Weak?

No. Circumstantial evidence is not automatically weak, and multiple independent findings can become highly informative when considered together.

Fingerprint on a Firearm

A fingerprint may suggest that someone touched the firearm but does not automatically establish when, why, or whether that person fired it.

Eyewitness Testimony

Evidence based on what a person reports seeing, hearing, or experiencing.

Is Eyewitness Testimony Always the Best Evidence?

No. Witnesses can be mistaken, memory can be distorted, details can be missed, and information may be unintentionally or intentionally changed.

How Eyewitness Testimony Should Be Evaluated

It should be evaluated critically and becomes stronger when supported by other evidence.

Admissibility

Whether evidence is legally allowed to be considered in court.

Who Determines Admissibility?

The court or judge, not the forensic scientist.

Requirements for Scientific Evidence in Court

Scientific evidence should be relevant and reliable.

Admissibility Hearing

A proceeding in which the court may evaluate whether scientific evidence and the method used to produce it are relevant and reliable.

Judge as Gatekeeper

The judge determines whether scientific or expert evidence meets the requirements to be admitted in court.

Frye Standard

A standard from Frye v. United States (1923) focusing on whether a scientific principle or technique has gained general acceptance within the relevant scientific community.

Frye Memory Trick

FRYE = Is the method generally accepted by scientists in that field?

Daubert Standard

A standard from Daubert v. Merrell Dow Pharmaceuticals (1993) in which the judge evaluates the relevance and reliability of scientific evidence.

Daubert Factors

Testability/falsifiability, peer review, standards, validation, potential error, and general acceptance.